1. Field of the Invention
The present invention relates to a vacuum robot, a vacuum motor for use in the vacuum robot, and a production method of the vacuum robot. More specifically, some preferred embodiments of the present invention relate to a work transferring vacuum robot for transferring a work in a vacuum environment, such as, e.g., in a semiconductor production apparatus or a crystal liquid production apparatus, a vacuum motor to be preferably used for driving a work transferring arm of the work transferring vacuum robot, a production method of the vacuum motor, and a work processing method using the vacuum robot.
2. Description of the Related Art
The following description sets forth the inventor's knowledge of related art and problems therein and should not be construed as an admission of knowledge in the prior art.
In recent years, various types of semiconductor production apparatuses and liquid crystal production apparatuses have been made available. The following explanation will be directed to a recently most common wafer processing apparatus as the related art.
FIG. 5 shows a typical wafer processing apparatus. This wafer processing apparatus is provided with a wafer transferring robot disposed approximately at the center of a transferring chamber, a plurality of processing chambers surrounding the transferring chamber, and a plurality of cassette chambers. This wafer processing apparatus is a sheet-feed multi-chamber type processing apparatus capable of continuously processing wafers one by one. FIG. 5 is a top view of the wafer processing apparatus. In this figure, the reference numeral “1” denotes a horizontal articulated type wafer transferring robot, “21” denotes a transferring chamber in which the wafer transferring robot 1 is installed, “22” denotes a cassette chamber, “C” denotes a wafer cassette for storing wafers, and “23” denotes a processing chamber.
The transferring chamber 21 and each cassette chamber 22, as well as the transferring chamber 21 and each processing chamber 23, are connected by an openable and closable gate valve 24 at the connecting openings 21a, 22a and 23a each having a certain opening size. The cassette chamber 22 has another opening 22b opened toward the outside. This opening 22b is closed by an openable and closable gate valve 25. Thus, the transferring chamber 21, each processing chamber 23, and each cassette chamber 22 can be held air-tight. Normally, each processing chamber 23 is always depressurized from atmospheric pressure to low pressure (hereinafter simply referred to as “vacuum”). In the same manner as in each processing chamber 23, the transferring chamber 21 is always depressurized to certain pressure and kept in a vacuum state.
The depressurization is performed by operating a pump to discharge the inner gas in each chamber. In order to keep the pressure in the transferring chamber 21 and each processing chamber 23 under a certain pressure, normally, a pump is kept driven to discharge the inner gas. The cassette chamber 22 is repeatedly changed from a vacuum state to an atmospheric state and vice versa as needed. At the time of introducing a wafer cassette C into the cassette chamber 22 from the outside, the cassette chamber 22 is kept at approximately the same pressure as atmospheric pressure by introducing, e.g., nitrogen gas from a gas introducing apparatus (not illustrated). At the time of opening the gate valve 24 connecting the cassette chamber 22 and the transferring chamber 21, in order to attain the same vacuum state as the transferring chamber 21, the cassette chamber 22 is depressurized to approximately the same pressure as that of the transferring chamber 21 using a pump or the like.
The cassette C in the cassette chamber 22 is provided with supporting shelves arranged at certain intervals so that unprocessed and/or processed wafers W can be stored on the supporting shelves in a multistage manner.
The wafer transferring robot 1 has a plurality of robot arms 2 and 3, and a hand 4 attached at the tip end of the robot arm 3. The wafer transferring robot 1 transfers a wafer W to a desired position with the wafer W disposed on the hand 4 by rotating and/or elongating/contracting the robot arms 2 and 3 and hand 4. In detail, the wafer transferring robot 1 is configured such that, after a certain gate valve 24 is opened, the robot arms 2 and 3 are elongated to insert the hand 4 into the cassette chamber 22 or the processing chamber 23 via the connecting opening 21a, 22a or 23a to carry in/out the wafer W. Furthermore, the wafer transferring robot 1 can perform a lifting and lowering operation for placing/loading a wafer W by lifting or lowering the robot arms 2 and 3 and the hand 4, and then advancing the hand 4 with respect to the wafer cassette C in a gap between wafers W in the wafer cassette C.
Now, the processing flow of the aforementioned sheet-feed multi-chamber type wafer processing apparatus 20 will be briefly explained. Initially, the wafer W is delivered in the cassette chamber 22 as a cassette unit. After vacuuming (discharging the air) the cassette chamber 22, the gate valve 24 disposed between the transferring chamber 21 and the cassette chamber 22 will be opened and then the wafer W in the cassette C will be carried into the transferring chamber 21 by the wafer transferring robot 1. Furthermore, the gate valve 24 disposed between the transferring chamber 21 and the processing chamber 23 will be opened and then the wafer W will be loaded into the processing chamber 23 by the wafer transferring robot 1. In the processing chamber 23, the wafer W is subjected to a processing step such as, e.g., film formation etching. Thus, each processing step is performed. After the final processing step, the wafer W will be carried out into the transferring chamber 21 by the wafer transferring robot 1, and then returned to the wafer cassette C in the cassette chamber 22. Thus, the wafer W will be subjected to series of processing steps in a predetermined atmosphere without being exposed to ambient air.
A conventional motor for driving robot arms of a wafer transferring robot to be driven in a vacuum environment of the aforementioned transferring chamber 21 is disclosed in Patent Documents, such as, e.g., U.S. Pat. Nos. 5,720,590 and 5,899,658. These Patent Documents disclose a motor for independently rotating two rotatable coaxial shafts connected to a plurality of robot arms by electromagnetic power. The aforementioned patent documents disclose two motor portions for driving two coaxial shafts. These two motor portions are disposed at different height positions about the center of the rotation axis.
The principal structural feature disclosed in these patent documents resides in that the rotor portion (the rotating portion of the motor to which magnets are attached) is located within the vacuum environment and that the electromagnetic generating stator portion (the non-rotating winding portion of the motor) is disposed in an atmospheric pressure environment. In detail, the rotor portion is encapsulated in a cylindrical portion of a cylindrical member (hereinafter referred to as a “can”) made of a thin plate, and the magnets of the rotor portion are arranged so as to face to the inner peripheral surface of the can. Since the inside of this can communicates with the vacuum environment such as the transferring chamber 21 in which the robot is installed, it follows that the rotor portion, the aforementioned coaxial shafts connected to the rotor portion and the robot arms are disposed in the vacuum environment of the transferring chamber 21.
On the other hand, the stator portion is disposed outside the can such that the winding of the stator portion surrounds the magnets of the rotor portion via the can. Since the external portion of the can is exposed to an atmospheric pressure environment, the entire stator portion is disposed in an atmospheric pressure environment. The stator portion generates electromagnetic power via the thin can to rotate the rotor portion. This in turn causes a rotation of the shaft, i.e., the robot arm, to thereby cause a desired operation of the wafer transferring robot. Since the winding portion of the stator portion is disposed in an atmospheric pressure environment, dust generated from the stator portion will not be introduced into the vacuum environment. Furthermore, no gas will be generated from the stator portion and introduced into the vacuum environment, and therefore the pressure of the vacuum environment can be further reduced.
However, the aforementioned conventional motor for a vacuum robot has the following drawbacks.
(1) It can be expected to produce an effect that even if the stator portion generates dust, the dust will not be introduced into the inner portion of the robot and/or into the vacuum chamber. However, a force (which is approximately the same as atmospheric pressure) caused by the pressure difference between the atmospheric pressure environment and the vacuum chamber is kept applied to the can separating the atmospheric pressure environment and the vacuum chamber, and therefore it is necessary to prevent the deformation and/or the breakage of the can. As a result, it is naturally required to maintain the strength of the can by increasing the thickness of the material of the cylindrical member constituting the can. This results in an increased size of the can, which in turn results in an increased body size of the robot including the motor portion.
(2) In order to increase the electromagnetic power of the motor, it is very effective to decrease the distance (electromagnetic gap) between the winding of the stator and the magnet of the rotor portion. However, since the can is located between the winding and the magnet, the electromagnetic gap increases as the thickness of the can increases, resulting in extremely decreased electromagnetic power. As is well known, keeping the electromagnetic gap even and narrow has a great effect on the motor performance.
(3) Although the winding of the stator portion is disposed at the atmospheric side, since the winding is made of a metallic wire, it can be oxidized by the moisture contained in the atmosphere to be rusted and corroded due to the dusting or the dew condensation. This may develop to break the insulation layer of the winding, causing the short circuit, which in turn results in an inoperable wafer transferring robot.
The description herein of advantages and disadvantages of various features, embodiments, methods, and apparatus disclosed in other publications is in no way intended to limit the present invention. Indeed, certain features of the invention may be capable of overcoming certain disadvantages, while still retaining some or all of the features, embodiments, methods, and apparatus disclosed therein.